The applicant of this application has filed a invention of the vehicle door lock device as shown in FIG. 1 with the Japanese Patent Office with a number of Patent application No. 1-160238 (corresponding to the U.S. Pat. application Ser. No. 07/537,970, now U.S. Pat. No. 5,005,392).
Depicting in a rear view of FIG. 1, the vehicle door lock device has a body (a) made of synthetic resin, a cover plate made of a metal sheet applied to the front side of the body (a), and a back plate (b) made of a metal sheet applied to the rear side of the body (a). These plates are secured integrally to the body (a) by means of screws. To the body (a), a latch engaged with a striker and a ratchet preventing the latch from reverse-rotating are rotatably journalled. At a position below the body (a), an actuator box (c) made of synthetic resin is placed, which actuator box is formed integrally with the body (a) or as a different structure. Explicitely, the actuator box (c) has a motor chamber (d) and a speed reducer (e).
According to the construction of the prior art, a lock lever (f) is rotatably journalled to the body (a) at the position between the motor chamber (d) and the back plate (b). A switch box (g) is fixed to the rear side of the back plate (b) through a screw (h). The switch box (g) is positioned so as to make an axis of the shaft (1) of the box (g) aligned with the center axis of the lock lever (f). A switch arm (j) is secured to the shaft (1) and an front end of the arm (j) is aligned with an oval hole (i) formed at a front end of the lock lever (f). An end portion of a rod (k) joined to a key cylinder in the door is engaged with the front ends of the oval hole (i) and the switch arm (j).
It is noted that the switch box (g) is attached to the lock device at the driver's door. When the lock lever (f) is rotated by a key manipulation or the like, the switch box (g) detects the rotation of the lock lever (f), outputting a control signal for locking or unlocking the lock devices in other doors.
The first problem of the conventional structure of the lock device resides in an overlapping arrangement of the switch box (g) and the lock lever (f) at a position below, the back plate (b). Explaining the arrangement more concretely, a guide rail extending perpendicularly so as to support glass panes of the doors is secured to the rear side of the back plate (b). The switch box (g) has, however, a thickness exceedingly thicker than the lever and arm, so that a large stepped portion is formed on the rear side of the back plate (b), causing a disadvantage in a securing work of the guide rail and effecting on the shape of the glass panes.
The second disadvantage of the conventional structure is the construction of the switch box (g). According to the structure in which the switch box (g) is fastened to the back plate (b) through a screw (h), the back plate (b) cannot be used as a bottom plate of the switch box (g). Consequently, the switch box (g) thickens by a thickness of the bottom plate (m). The switch, box (g) disadvantageously is apt to be displaced at its securing position, since it is fastened by the screw (h) after it is temporarily placed in position.